The invention relates to an electrically controlled fuel injection pump for internal combustion engines, especially for direct fuel injection in engines having externally supplied ignition, in which a plurality of pump pistons, driven at a constant stroke by drive cams and each guided in one cylinder bore, pump the fuel, brought to injection pressure in an associated pump work chamber, to injection valves.
A fuel injection pump of this type is found for instance in U.S. Pat. No. 4,459,963 to Straubel et al. In this known fuel injection pump, two side-by-side pump pistons are provided in one fuel injection pump housing, the pump pistons each being driven by a separate camshaft. Each pump pistons pump into a single fuel injection line associated with it and leading to a fuel injection valve of the associated engine. Control of the injection quantity is effected via a common overflow conduit, which can be opened to a relief space with a magnetic valve. The pump pistons also execute their supply strokes in alternation, and to prevent the quantity of fuel pumped by one pump piston at high pressure from being capable of flowing out to the relief side during the intake or fill stroke of the other pump piston, a slide valve control is provided. The pump piston itself, with a control edge, acts as the valve slide. Alternatively, check valves are also provided, in the fuel fill line to the various pump work chambers, among other locations. Thus the known fuel injection pump is embodied as an in-line injection pump, with each pump piston serving to supply fuel to one injection location.
In accordance with an earlier proposal, not yet published (German Patent Application P 38 04 025.8), a fuel supply system to a plurality of injection valves was created in which a plurality of pump pistons can cooperate simultaneously, to attain a high injection pressure for an injection valve or injection location. The smaller structure of this earlier proposal resulted from the fact that a plurality of pump pistons could be driven by a common cam, and that the valve control already provided in principle in U.S. Pat. No. 4,459,963 was replaced by the substantially simpler control using a rotary slide valve. A desired injection pressure could be built up in the central guide of such a rotary slide valve, and depending on the rotational position of the rotary slide valve, injection valves were acted upon by the pump pressure until such time as a suitable diversion took place, for instance by the opening of a magnetic valve to a relief chamber. In this known construction, variously long lines led to the various connections of the rotary slide valve, beginning at the work chambers of the pump pistons, and especially at higher rpm and higher injection pressures, produced conditions that could not be precisely defined.